Oscillator and telecommunications system with such an oscillator

ABSTRACT

The oscillator integrated into a chip can generate an electrical clock signal with a reference signal, wherein the chip contains the following components: at least one laser transmitter, which can generate two coherent light signals with a differing optical transmission frequency, a coupler, in order to merge the two light signals, an electromagnetic converter, which can generate an electrical signal, whose frequency corresponds to the distance between the two transmission frequencies, a frequency divider, which can divide the frequency of the electrical signal in order to deliver a clock signal with a lower frequency. The oscillator can be inserted into a SIM card, for example, in order to make possible a non-falsifiable determination of the connection duration.

This application is the National Phase of International ApplicationPCT/CH98/00506 filed Dec. 1, 1998 which designated the U.S. and thatInternational Application was not published under PCT Article 21 (2) inEnglish.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a chipcard with an oscillator (8) integratedhereon. In particular, the invention also relates to telecommunicationssystems and telecommunications methods, which use such a chipcard.

2. Description of Related Art

Many portable, electronic devices require a miniaturized oscillator,which can generate a signal with a stable frequency. Crystal oscillatorsare frequently used for this purpose since they need little current andcan easily be integrated into small devices, for example wristwatches.

A great many attempts have already been made to integrate a crystaloscillator together with various other electronic components, forexample a frequency divider, into a single chip. The patent documents DE4011795, U.S. Pat. No. 5,406,230 and U.S. Pat. No. 5,229,640, forexample, describe various solutions to achieve this object. In practice,many difficulties still have to be overcome before a really reliable,inexpensive and miniaturized crystal oscillator comes on the market.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the invention to propose an improvedoscillator, which can be integrated into a chip of minimal dimensions,and which can be inserted, for example, into a chipcard, including achipcard of the “plug-in” format, as are used, for example, in mobileradio telephones (SIM cards).

Another object is to propose a new integrated oscillator which cangenerate a reference signal with a frequency that cannot be falsified,and which can be used, for example, for secure applications where anon-falsifiable determination of the time is required.

A further object is to achieve a chipcard with an integrated oscillator,with which the duration of certain processes, for example the durationof telephone calls in the case of a SIM card, can be established.

According to the invention these objects are attained with the aid of adevice as described in the independent device claim and with a method asdescribed in the independent method claim, various variants beingdescribed in the dependent claims.

In particular these objects are achieved with the aid of a newintegrated oscillator with which an electrical signal is generated froman interference between two coherent light signals, the light signalsbeing generated with one or more integrated laser transmitters.

R. P. Braun et al. describe in “Low-Phase-Noise Millimeter-WaveGeneration at 64 GHz and Data Transmission Using Optical SidebandInjection Locking,” IEEE Photonics Technology Letters, Vol. 10, No. 5,May 1998, the possibility of generating signals with a frequency of onlysome megahertz from an interference between two laser signals. Thedescribed device is intended for base stations in a mobile radionetwork; however, it is not indicated in this document that integratedlaser sources can also be used.

Other experiments in generating microwave signals from an interferencebetween laser signals have also been described by R. P. Braun et al. in“Optical Harmonic Upconversion for Microwave Generation in BidirectionalBroadband Mobile Communication System, ” Electronics Letters, Vol. 33,No. 22, Oct. 23^(rd) 1997, and by R. P. Braun et al. in “OpticalMicrowave Generation and Transmission Experiments in the 12- and 60-GHzRegion for Wireless Communications,” IEEE Transactions on MicrowaveTheory and Techniques, Vol. 46, No. 4, Apr. 1998. Although all thesedocuments concern the generation of signals in the microwave range (forexample signals with a frequency of 12 or 60 GHz), signals with a lowerfrequency can also be generated with the same principle, for examplesignals which can be processed by conventional, digital logic circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood with the aid of thedescription, given as an example, and illustrated by the figures:

FIG. 1 is a block diagram showing an oscillator according to theinvention, and

FIG. 2 is a block diagram showing an identification card according tothe invention in a mobile communications system.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows diagrammatically the most important components of anoscillator 8 according to the invention. The oscillator 8 comprises inthe example shown two integrated laser transmitters 1, 2, which generatetwo coherent light signals with two close-together optical transmissionfrequencies. Integrated lasers, which are achieved with semiconductortechnology, and which can be integrated into chips, are already known,and were described, inter alia, by Jens Uwe Nöckel in the Neue ZürcherZeitung of Jun. 24^(th) 1998, page 69, or by Christian Wyss in the NeueZüircher Zeitung of Aug. 12^(th) 1998. They are based, for example, onan oval resonator of about 10 to 80 micrometers in diameter or ondiode-pumped solid state lasers.

The transmitted light beams are directed to an optional optical coupler3, which is also integrated into the chip, and which can simply consistof, for example, a transparent glass element. An interference betweenthe two light beams from the two laser sources 1, 2 is generated in thisway in the coupler 3, the frequency of the resultant electromagneticwave corresponding to the difference between the optical transmissionfrequency of the two laser transmitters 1, 2.

If a frequency separation of between 100 MHz and 10 GHz, preferablyhowever between 500 MHz and 1 GHz, is selected, an electromagnetic waveis generated in the coupler 3 with a wavelength of between approximately0.1 and 1 millimeter. This wave is received by an electromagneticconverter 4, which preferably consists of a simple integrated receivingantenna, and supplies an initial current with a frequency correspondingto the frequency separation between the two transmitted light beams.

The high frequency signal, which is generated by the antenna 4, is givento a frequency divider 5, which, at its output, emits a digitalreference signal CK with a lower frequency, for example a 32 KHz signal.This signal can be used, for example, for the synchronization of clocks,watches or time-measuring devices.

The transmission frequency of the two laser transmitters 1, 2 ispreferably stabilized with a frequency stabilizing element 6, which, forexample, controls the current injected in the two laser transmitters 1,2. In a variant, a Peltier element (not shown) is used to controlelectronically the temperature of the chip and of the two transmitters1, 2, so that the transmission frequency remains stable. The injectedcurrent in the Peltier element is likewise preferably controlled by thestabilizing element 6.

The stabilizing element 6 is preferably controlled by a feedback signal,which is generated by a frequency voltage converter 9, whereby theconverter 9 delivers a voltage which is proportional to the frequency ofthe signal CK at the output of the frequency divider 5. In this way thetransmission frequency of the two laser transmitters 1, 2 is controlledby the frequency of the signal CK at the output of the entire system.

In a further embodiment variant of the invention, a single lasertransmitter is used, which generates two different close-togetherfrequencies (dual mode laser). In this case most of the frequencydeviations or jumps of the two laser beams occur simultaneously, so thatthe frequency separation remains extraordinarily stable.

Further methods of obtaining an interference between two coherent laserbeams from a single light source are described, inter alia, by R. P.Braun et al. in “Optical Millimeter-Wave Systems for Broadband MobileCommunications, Devices and Techniques, ” International Zurich Seminaron Broadband Communications-Accessing, Transmission, Networking, ETHZurich, Switzerland, Feb. 1998. Known, for example, aresideband-modulation techniques and mode locked lasers (MLL).

FIG. 2 shows an identification card 13, for example a SIM card formobile radio devices, which contains an oscillator 8 according to theinvention. The reference signal CK, which is generated by the oscillator8 described above, is emitted at the clock input of a counter 16 ofknown type. At the output, the counter gives a time indication t, whichdepends upon the number of received pulses of the signal CK. The timeindication can correspond, for example, to the absolute time or to theduration since the beginning of a process, for example the duration of atelephone connection.

The value in the counter 16 can be initialized with an initializationvalue stored in an initialization register 10, for example, uponswitching on or logging the card into a telecommunications network 14.The initialization value in the initialization register can be remotelyloaded from a time server 15, which can send time documents to the card13. The time documents are transmitted preferably by means of USSD shortmessages via a GSM mobile radio network 14, and are filed in a protectedmemory zone 11 of the card 13; other types of data messages and oftelecommunications systems can also be used, however. Cryptographicmechanisms are preferably used in order to sign the transmitted messagesand to prevent falsifications. The Swiss patent application No. 367/98describes other processes to set the time t in the counter 16 whenlogging in the card.

The counter 16 and the registers 10 and 11 are preferably located in aprotected zone 12 of the card 13, so that the indicated value t emittedby the counter 16 cannot be falsified. Of course the user also has nopossibility of influencing the frequency signal CK emitted by theoscillator 8 or of setting it from outside.

The time indication t delivered by the counter 16 can be used, forexample, to determine the duration and the price of telephone calls.This way the determined amount can be booked immediately against theaccount of a prepaid SIM card, or can be packed in a signed document andtransmitted to a financial services provider (bank or network operator).The card according to the invention can also be used to measure theduration of other processes in the card 13, for example the duration ofuse of certain services or applications or the use of resources notresponsible for traffic flow.

It is also possible, moreover, to use chipcards for applications otherthan mobile telephony. Such chipcards can also be used, for example, forpay TV systems or in networked computers, for example to make out ause-time-dependent bill, which depends upon the time of use or theduration of use.

The oscillator 8 cannot supply a reference signal CK until it is fedwith electricity, for example when the card is inserted into aswitched-on mobile device. The counter 16 must then be set again aftereach switching on of the mobile device. To avoid this drawback, it isalso possible to provide the card with an energy store, for example abattery, so that the card is electrically autonomous.

One skilled in the art will understand that the oscillator according tothe invention can also be used in other portable mobile devices, forexample to generate a reference signal in a clock.

What is claimed is:
 1. A chipcard with an oscillator integrated into achip, the oscillator being arranged to generate an electrical clocksignal with a reference frequency, wherein said oscillator comprises thefollowing components: at least one laser transmitter arranged togenerate two coherent light signals with a differing opticaltransmission frequency, an electromagnetic converter arranged to convertthe wave generated from an interference between the two said lightsignals into an electrical signal, and a frequency divider arranged todivide the frequency of said electrical signal in order to emit a clocksignal with a lower frequency.
 2. The chipcard according to claim 1,wherein said at least one laser transmitter consists of a semiconductormicro-laser.
 3. The chipcard according to claim 2, wherein said at leastone semiconductor micro-laser contains an oval resonator.
 4. Thechipcard according to claim 2, wherein said at least one semiconductormicro-laser contains an optically pumped, solid-state laser.
 5. Thechipcard according to claim 1, wherein said oscillator contains twodifferent laser transmitters, which generate two coherent light signalswith differing optical transmission frequencies.
 6. The chipcardaccording to claim 1, wherein the said oscillator contains a singlelaser transmitter, which has two transmission modes.
 7. The chipcardaccording to claim 1, further comprising a stabilizing element tostabilize the said optical transmission frequency of the said at leastone laser transmitter.
 8. The chipcard according to claim 7, whereinsaid stabilizing element is controlled with the frequency of the saidclock signal.
 9. The chipcard according to claim 7, further comprising aPeltier element in order to control the temperature of said at least onelaser transmitter.
 10. The chipcard according to claim 9, wherein thecurrent, which is injected into said Peltier element, is dependent uponthe frequency of said clock signal.
 11. The chipcard according to claim1, further comprising a counter, and said clock signal is applied at theclock impulse input of said counter.
 12. The chipcard according to claim11, further comprising an initialization register in which aninitialization value for said counter can be stored.
 13. The chipcardaccording to claim 12, wherein the chipcard is an identification card toidentify subscribers in a telecommunications network.
 14. The chipcardaccording to claim 13, wherein the value in the said initializationregister can be changed with short messages transmitted via the saidtelecommunications network.
 15. The chipcard according to claim 13,further comprising an energy store which feeds the oscillator.
 16. Thechipcard according to claim 13, wherein said registers are stored in anarea of the identification card not accessible to the subscriber.
 17. Abilling method for billing a call of a subscriber identified with anidentification card in a telecommunications network to the subscriber,comprising the steps of: determining the duration of the call using atime-measuring device integrated into the identification card, thetime-measuring device comprising an integrated oscillator for generatingan electrical clock signal with a reference frequency, the referencefrequency being generated from an interference between two coherentlaser signals, and the measured duration of the call being determinedbased on the reference frequency; and determining the amount to bebilled based on the duration of the call measured with the timemeasuring device.
 18. The billing method according to claim 17, whereina time controller in the telecommunications network checks the set timeafter each logging in of an identification card, and, if the time is notcorrectly set, transmits a time document to this identification card.19. The billing method according to claim 18, wherein the transmittedtime documents are electronically signed.
 20. The billing methodaccording to claim 17, wherein the determined amounts are bookeddirectly against a prepaid account in the identification card.
 21. Thebilling method according to claim 17, wherein the determined amounts arepacked in a signed document, and are transmitted to a is financialservices provider.
 22. The billing method according to claim 17, whereinthe use of resources in the identification card not responsible for thecommunications transaction are billed as a function of the tariff tablesand the said time-measuring device.
 23. A chipcard comprising: anoscillator integrated into a chip, the oscillator including, means forgenerating two coherent light signals with a differing opticaltransmission frequency, means for converting the wave generated from aninterference between the two said light signals into an electricalsignal, and means for dividing the frequency of said electrical signalin order to emit a clock signal with a lower frequency.